WO2003054384A1

WO2003054384A1 - Fuel-injection device, fuel system and internal combustion engine

Info

Publication number: WO2003054384A1
Application number: PCT/DE2002/004204
Authority: WO
Inventors: Friedrich Boecking
Original assignee: Robert Bosch Gmbh
Priority date: 2001-12-08
Filing date: 2002-11-14
Publication date: 2003-07-03
Also published as: DE10160490B4; DE10160490A1

Abstract

An injector (26) for internal combustion engines with direct injection comprises a housing (34), provided with a cavity (40) and at least one fuel outlet (46). A valve element (42) is located in the cavity (40) and comprises a conical annular surface (74) in one end region (72). Said surface co-operates with a valve seat (82) that is fixed to the housing. A fluidic connection (70) connects a high-pressure connection to a flow chamber (88) that is located directly upstream of the valve seat (82). The aim of the invention is to improve the emission behaviour of internal combustion engines. To achieve this, the fluidic connection (70) opens into the flow chamber (88) by means of at least one inlet (86a, 86b), which lies in the vicinity of the valve seat (82). In addition, a first section (76) of the conical annular surface (74), said section lying between the inlet (86a, 86b) and the valve seat (82) in the end region (72) of the valve element (42), forms an angle of between 10° and 35°, preferably between 15° and 30° with an opposing surface (84) of the housing (34).

Description

Fuel injector, fuel system and internal combustion engine

State of the art

The invention initially relates to a fuel injection device, in particular an injector for internal combustion engines with direct injection, with a housing which comprises a recess and at least one fuel outlet opening, with a valve element which is arranged in the recess and comprises a conical annular surface at one end region , which cooperates with a valve seat fixed to the housing, and with a fluid connection which connects a high-pressure connection to a flow space arranged immediately upstream of the valve seat.

Such a fuel injection device is known from DE 199 33 328 AI. It is a common rail injector which is operated hydraulically. A valve needle is pressed against a valve seat by a valve spring. A pressure surface acting in the opening direction of the valve needle is constantly subjected to high fuel pressure, which in turn is provided by a fuel collecting line ("rail"). When the valve needle is closed, the pressure prevailing in the fuel collecting line is also present on another pressure surface acting in the closing direction of the valve needle. A control valve allows this pressure area acting hydraulic pressure can be reduced. Then the valve needle moves against the action of the valve spring and lifts off the valve seat. As a result, a flow space arranged upstream of the valve seat is connected to a fuel outlet opening, so that fuel can escape from the fuel injection device.

Such fuel injection devices are used in internal combustion engines with direct fuel injection. In these, the fuel is injected directly into a combustion chamber assigned to the fuel injection device. The very high fuel pressure to be provided in the fuel manifold is usually generated by a pre-feed pump and a main feed pump.

The object of the present invention is to develop a fuel injection device of the type mentioned at the outset in such a way that the nitrogen oxide emissions of an internal combustion engine which is equipped with such a fuel injection device are reduced.

This object is achieved in a fuel injection device of the type mentioned at the outset in that the fluid connection opens into the flow space via at least one inlet opening which is located in the vicinity of the valve seat, and in that a first section of the conical annular surface arranged between the inlet opening and the valve seat on End region of the valve element with an opposite surface of the housing encloses an angle of 10 'to 35', preferably 15 'to 30'.

Advantages of the invention

The fuel injection device according to the invention has the advantage that the pressure curve downstream of the valve seat can be configured in a desired manner depending on the stroke of the valve element during the opening and closing process. In this way it can be avoided, for example, that when the fuel injection device is opened immediately after the valve element is lifted off the valve seat, there is a steep pressure increase downstream of the valve seat.

According to the invention, this was recognized as a possible cause for undesired nitrogen oxide emissions in internal combustion engines. Such undesirable nitrogen oxide emissions are to be expected in particular in commercial vehicle systems if the pressure rises very sharply with the stroke of the valve element downstream of the valve seat when the valve element is opened.

A prerequisite for the desired throttling immediately after the valve element is lifted off the valve seat is that the fuel flows into the flow space arranged immediately upstream of the valve seat via an inlet opening located just upstream of the valve seat. Furthermore, the angle that the two opposing boundary surfaces of the flow space make directly in front of the valve seat must be very small.

Both measures make it possible that when the valve element lifts off the valve seat, the pressure curve downstream of the valve seat initially depends on the increasing gap between the valve seat and the valve element, but the pressure increase over the stroke downstream of the valve seat becomes flatter as the stroke movement continues, since the flow is then restricted by the distance between the conical ring surface at the end region of the valve element and the opposite one Area of the housing is determined.

Since these two surfaces are almost parallel and the clear width between the two surfaces in the course of the opening movement of the valve element depends on the conicity of the end region of the valve element, the throttle characteristic can be set in the desired manner via the stroke in the fuel injection device according to the invention. that the pressure rises comparatively flat downstream of the valve seat. It should be expressly pointed out here that the advantages according to the invention can be achieved in fuel injection devices with blind hole nozzles as well as with seat hole nozzles.

Advantageous developments of the invention are specified in the subclaims.

In a first development, it is proposed that a second section of the conical ring surface at the end region of the valve element, which is arranged immediately downstream of the valve seat, encloses an angle with the opposite surface of the housing, which is somewhat larger than the angle between the first section of the conical Ring surface and the opposite housing surface.

In this way, a further "throttle stage" is created, the effect of which appears when the valve element has moved so far that the two throttle effects described above decrease. As a result of the aforementioned configuration of the second section of the conical ring surface at the end region of the valve element, an even flatter region than the two previous regions is created within the stroke throttle curve, which links the flow quantity with the stroke of the valve element. The effect according to the invention of reducing the nitrogen oxide emissions which can occur during the operation of an internal combustion engine is further enhanced in this development.

The fuel injection device is particularly compact when the fluid connection comprises a flow channel which runs in the valve element overall in its longitudinal direction.

It is also proposed that the inlet opening be arranged in the first section of the annular surface at the end region of the valve element. Such a fuel injection device also has a very compact design and enables a flow profile which is favorable with regard to the desired throttle properties in the flow space arranged upstream from the valve seat.

If a ring edge of the inlet opening is rounded at least in some areas, this can also influence the throttling behavior. This applies in particular to the throttling effect which occurs between the first section of the conical annular surface of the valve element and the opposite surface of the housing.

It is also proposed that a flow cross section of the fuel outlet opening is smaller than a flow cross section of the fluid connection. In this way, a "throttle stage" can be created again, the throttling effect of which is completely independent of the stroke of the valve element. This "throttle stage" formed by the flow cross section of the outlet opening acts with a comparatively large stroke of the valve element and leads to a horizontally extending section of the stroke-throttle curve. The measures according to the invention are very well suited for a fuel injection device in which the valve element is actuated hydraulically. In a specific embodiment, it is proposed that the fuel injection device include a hydraulic control chamber, which is delimited by a pressure surface acting in the longitudinal direction of the valve element, which is formed by at least one shoulder on an outer peripheral wall of the valve element. The control chamber is thus located radially outside relative to the valve element. The high-pressure sealing of the housing of the fuel injection device is considerably simplified by this measure.

However, it is also possible for the valve element to be actuated by a magnetic or a piezo actuator. With both designs, relatively short switching times can be achieved with a simple structure.

The invention also relates to a fuel system with a fuel tank, with at least one fuel injection device that injects the fuel directly into the combustion chamber of an internal combustion engine, with at least one high-pressure fuel pump, and with a fuel manifold to which the fuel injection device is connected ,

In order to be able to realize low nitrogen oxide emissions in an internal combustion engine which is equipped with such a fuel system, it is proposed that the fuel injection device be designed in the above manner.

The invention further relates to an internal combustion engine with at least one combustion chamber into which the fuel is injected directly. To the emission behavior of such To improve an internal combustion engine, it is proposed that it has a fuel system of the above type.

drawing

A particularly preferred exemplary embodiment of the present invention is explained in detail below with reference to the accompanying drawing. The drawing shows:

Figure 1 is a schematic diagram of a

Internal combustion engine with multiple fuel injectors;

Figure 2 is a partial longitudinal section through one of the

Fuel injectors of Figure 1;

Figure 3 is an enlarged partial section through a

End region of the fuel injection device of Figure 2;

Figure 4 is a further enlarged view of the

End region of the fuel injection device of Figure 3; and

FIG. 5 shows a diagram in which the fuel

Injection device of Figure 2 is shown amount of fuel over a stroke of a valve element.

Description of the embodiment

In FIG. 1, an internal combustion engine bears the reference number 10 overall. It comprises a fuel system 12. Fuel is stored in a fuel tank 14 of the fuel system 12. An electrically driven fuel pump 16 delivers fuel from the fuel tank 14 to a high-pressure fuel pump 18. This is driven directly in a manner not shown in FIG. 1, for example, by a camshaft of the internal combustion engine 10. The high-pressure fuel pump 18 delivers the fuel under high pressure into a fuel manifold 20. In this, the fuel can be stored under high pressure during operation of the internal combustion engine 10.

High-pressure lines 22 lead to high-pressure connections 24 of fuel injection devices 26. These are injectors, which inject the fuel directly into combustion chambers 28. Low-pressure connections 30 of the injectors 26 are connected to a low-pressure return line 32, which leads back to the fuel tank 14. The operation of the internal combustion engine 10 and the fuel system 12 is controlled or regulated overall by a control and regulating device, not shown in the figure.

The exact structure of the injector 26 can be seen from FIGS. 2 and 3 (not all reference numerals are shown in FIG. 2 for reasons of illustration): The injector then comprises a housing 34, of which a nozzle body 36 and an intermediate disk 38 are shown in FIG , These are braced against each other by a nozzle clamping nut, not shown in the figure. There is a blind hole-like recess 40 in the nozzle body 36. A valve element 42 is inserted into this. In FIG. 2, the recess 40 is closed at the bottom by an injection cone 44, in which a fuel outlet opening 46 is present. The valve element 42 extends in the longitudinal direction coaxially to the recess 40. It has a section 48 with a larger diameter in the manner of an annular collar approximately in its axial center. A valve spring 50 is supported on this and acts on a sleeve 52 against the intermediate disk 38. The seal between the sleeve 52 and the intermediate disk 38 takes place in that the upper edge of the sleeve 52 in FIG. 2 is designed as a cutting edge 54.

The section 48 of the valve element 42 works together with the recess 40 in the nozzle body 36 in sliding play, but is fluid and pressure-tight. A hydraulic control chamber 56 is present between the section 48, the recess 40, the intermediate disk 38, the sleeve 52 and the region of the valve element 42 located above the section 48 in FIG. An upper end face of section 48 of valve element 42 in FIG. 2 forms a pressure surface 58 acting in the longitudinal direction or closing direction of valve element 42.

The hydraulic control chamber 56 can be connected to the low-pressure connection 30 and subsequently to the low-pressure return line 32 via a discharge throttle 60 by means of a control valve 62. This will be discussed in more detail below. A channel 64 in the intermediate disk 38 connects the high-pressure connection 24 to an upper flow space 66 formed between the intermediate disk 38, an upper axial end surface 64 of the valve element 42 in FIG. 2, and the sleeve 52.

An inlet throttle 68 in the sleeve 52 in turn connects the upper flow chamber 66 to the hydraulic control chamber 56. In the longitudinal direction of the valve element 42 there is a flow channel 70 coaxial with the longitudinal axis of the valve element 42. This leads from the upper flow chamber 66 in Valve element 42 to an end region 72 of valve element 42 which is lower in FIG. 2. The exact design thereof can be seen in detail in FIGS. 3 and 4:

A conical annular surface 74 is present at the end region 72 of the valve element 42, so that the lower end of the valve element 42 in FIGS. 2 to 4 tapers conically. The conical ring surface 74 comprises a radially outer section 76, which encloses a smaller angle with the longitudinal axis of the valve element 42 than a radially inner section 78. A sealing edge 80 is present between the two sections 76 and 78 of the conical ring surface 74. This works together with a valve seat 82 which is formed on a likewise conical ring surface 84 of the injection cone 44 of the nozzle body 36.

The flow channel 70 running in the valve element 42 branches in the area of the lower end area 72 into two separate channels (without reference numerals), which lead to inlet openings 86a and 86b. The inlet openings 86a and 86b are arranged diametrically opposite in the radially outer section 76 of the conical ring surface 74. The branches of the flow channel 70 run approximately at a right angle to the radially outer section 76 of the conical ring surface 74.

The radially outer section 76 of the conical annular surface 74 at the lower end region 72 of the valve element 42 and the conical annular surface 84 in the injection cone 44 of the nozzle body 36 delimit a flow space 88 located immediately upstream from the valve seat 82 or the sealing edge 80. Downstream from the valve seat 82 or the Sealing edge 80 is between the radially inner section 78 of the conical ring surface 74 at the lower end region 72 of the valve element 42 and a wall of the injection cone 44 second flow space 90 available.

The position of the fuel outlet opening 46 is shown in FIG. 3 on the left side using the example of a seat hole nozzle, in FIG. 3 on the right side using the example of a blind hole nozzle. The flow cross-section d2 of the fuel outlet opening 46 is in any case smaller than the sum of the flow cross-sections dl of the branches of the flow channel 70 in the valve element 42. The radially outer region of the inlet openings 86a and 86b in FIGS. 3 and 4 is, as in particular from FIG. 4 can be seen, formed with a curve 92.

The angle which the radially outer section 76 of the conical ring surface 74 forms with the conical ring surface 84 of the injection cone 44 of the nozzle body 36 is very small and is denoted by α1 in FIG. It is advantageously approximately 10 'to 35', an angle α1 in the range between 15 'and 30' is particularly advantageous. It should be pointed out here that in FIGS. 2 to 4 the angles are shown exaggerated for reasons of drawing technology. The angle which the radially inner section 78 of the conical annular surface 74 of the end region 72 of the valve element 42 forms with the conical annular surface 84 of the injection cone 44 of the nozzle body 36 is designated α2 in FIG. 4 and is somewhat larger than the above angle α1.

The injector 26 works as follows:

If no fuel is to be injected from the injector 26, the control valve 62 is closed. In this case, the same pressure prevails in the control chamber 56 as in the flow chambers 66 and 88, namely the full system pressure prevailing in the fuel rail. Due to the force by the valve spring 50 and by the Hydraulic force, which acts on the pressure surface 58 and acts in the closing direction of the valve element 42, the valve element 42 is pressed with the sealing edge 80 against the valve seat 82. The flow space 88 is thus separated from the flow space 90 and no fuel can escape from the fuel outlet opening 46.

If an injection of fuel into a combustion chamber 28 is desired, the control valve 62 opens. This allows fuel to flow out of the control chamber 56 via the outlet throttle 60 into the low-pressure return line 32. Since the inlet throttle 68 is smaller than the outlet throttle 60, the fuel cannot flow into the control chamber 56 at the same speed, so that a pressure drop occurs in the latter. This also reduces the closing force acting on the pressure surface 58.

At the same time, the full system pressure continues to act on the radially outer section 76 of the conical annular surface 74 located upstream from the sealing edge 80. When the hydraulic force resulting on the outer section 76 of the conical ring surface 74 of the valve element 42 exceeds the closing force of the valve spring 50 and the hydraulic force acting on the pressure surface 58, the valve element 42 lifts off with its sealing edge 80 from the valve seat 82. The fuel can thus pass from the flow space 88 into the flow space and from there through the outlet opening 46 into the combustion space 28 assigned to the injector 26. The course of the flow quantity dm / dt over a stroke h of the valve element 42 can be seen from FIG. 5:

Immediately after the sealing edge 80 of the valve element 42 has been lifted off the valve seat 82, the throttling of the flow quantity dm / dt is essentially determined by the gap that results between the sealing edge 80 and the valve seat 82. The corresponding area in the diagram 5 bears the reference number 94. It can be seen that immediately after the sealing edge 80 has been lifted off the valve seat 82, a very steep increase in the flow quantity and thus also in the pressure in the flow space 90 can be observed.

In the further course of the lifting movement of the valve element 42, the disk-ring-shaped flow channel resulting between the radially outer section 76 of the conical ring surface 74 and the conical ring surface 84 of the injection cone 44 begins to develop a throttling effect which is stronger than the above-mentioned throttling effect. The corresponding section bears the reference symbol 96 in FIG. 5. It can be seen that the increase in the flow rate dm / dt over the stroke h is less pronounced in section 96 than in section 94. Accordingly, the pressure in flow chamber 90 also rises less strongly.

If the valve element 42 moves still further, the throttling which is caused by the flow cross section which results between the inner section 78 of the conical annular surface 74 and the conical annular surface 84 of the injection cone 44 increases. The corresponding section has the reference symbol 98 in FIG. 5. It is again flatter than section 96, i.e. that the pressure increase in the flow space 90 is even lower.

When the valve element 42 has lifted its sealing edge 80 far enough from the valve seat 82, only the fuel outlet opening 46 throttles. In this case, the flow quantity dm / dt is independent of the stroke h of the valve element 42, namely constant. Accordingly, there is also no further pressure increase in the flow space 90 of the injector 26. The corresponding section of the curve has the reference symbol 100 in FIG. 5. The injection of fuel by the injector 26 is ended by the control valve 62 closing. As a result, the pressure in the control chamber 56 rises again and the valve element 42 is pressed again with the sealing edge 80 against the valve seat 82. The course of the flow quantity dm / dt over the stroke h or the course of the pressure in the flow space 90 is then reversed from the course described above.

In the injector 26 shown in FIGS. 2 to 4, the movement of the valve element 42 is controlled hydraulically. However, it goes without saying that the advantage of a relatively flat pressure curve over the stroke of the valve element can also be realized with an injector whose valve element is moved, for example, by a magnetic actuator or by a piezo element.

Claims

Expectations

1. Fuel injection device (26), in particular injector for internal combustion engines (10) with direct injection, with a housing (34) which comprises a recess (40) and at least one fuel outlet opening (46) with a valve element

(42), which is arranged in the recess (40) and at one end region (72) comprises a conical ring surface (74) which cooperates with a valve seat (82) fixed to the housing, and with a fluid connection (70) which connects a high pressure connection ( 24) connects to a flow space (88) arranged immediately upstream of the valve seat (82), characterized in that the fluid connection (70) via at least one inlet opening

(86a, 86b), which lies in the vicinity of the valve seat (82), opens into the flow space (88), and that a first section (76) of the conical annular surface (76) arranged between the inlet opening (86a, 86b) and the valve seat (82) 74) at the end region (72) of the valve element (42) with an opposite surface (84) of the housing (34) forms an angle (αl) of 10-35 ', preferably 15-30'.

2. Fuel injection device (26) according to claim 1, characterized in that a second section (78) of the conical annular surface (74) at the end region (72) of the valve element (42), which is arranged immediately downstream of the valve seat (82), with the opposite surface (84) of the housing (34) an angle (α2) includes, which is slightly larger than the angle (αl) between the first portion (76) of the conical ring surface (74) and the opposite housing surface (84).

3. Fuel injection device (26) according to one of claims 1 or 2, characterized in that the fluid connection comprises a flow channel (70) which runs in the valve element (42) overall in its longitudinal direction.

4. Fuel injection device (26) according to claim 3, characterized in that the inlet opening (86a, 86b) is arranged in the first section (76) of the annular surface (74) at the end region (72) of the valve element (42).

5. Fuel injection device (26) according to one of the preceding claims, characterized in that an annular edge of the inlet opening (86a, 86b) has a rounded portion (92) at least in regions.

6. Fuel injection device (26) according to one of the preceding claims, characterized in that a flow cross section (d2) of the fuel outlet opening (46) is smaller than a flow cross section (dl) of the fluid connection (70).

7. Fuel injection device (26) according to one of the preceding claims, characterized in that the valve element (42) is actuated hydraulically.

8. Fuel injection device (26) according to claim 7, characterized in that it comprises a hydraulic control chamber (56), which is bounded by a pressure surface (58) acting in the longitudinal direction of the valve element (42), which by at least one shoulder on a outer peripheral wall of the valve element (42) is formed.

9. Fuel injection device according to one of claims 1 to 6, characterized in that the valve element is actuated by a magnetic or a piezo actuator.

10. Fuel system (12) with a fuel tank (14), with at least one fuel injection device (26) which injects the fuel directly into the combustion chamber (28) of an internal combustion engine (10) with at least one high-pressure fuel umpe (18) , and with a

Fuel manifold (20) to which the fuel injection device (26) is connected, characterized in that the fuel injection device (26) is designed according to one of claims 1 to 9.

11. Internal combustion engine (10), with at least one combustion chamber (28) into which the fuel is injected directly, characterized in that it has a fuel system (12) according to claim 10.